The present invention relates to a new and improved method of, and apparatus for, carrying out thermoanalytical investigations.
Apparatus for thermoanalytical investigations, especially at low temperatures, have been proposed to the art, and which apparatus is of the type comprising an oven or furnace providing a chamber for receiving a sample or article which is to be investigated, and a device for ascertaining the temperature of the sample or a parameter of the sample which characterises the temperature thereof. The temperature in the sample chamber is controlled to a desired or reference value by a control assembly including a device for pre-setting a desired or reference value. There is further provided a heater for heating the sample chamber and a sensor for measuring the temperature in the sample chamber. Adjacent to but separated from the sample chamber is a chamber for receiving a flowing cooling medium or coolant which is supplied from a cooling medium tank or reservoir.
Such apparatus are used for investigating physical and/or chemical processes as a function of temperature, in other words, for example, apparatus for differential thermal analysis (hereinafter simply conveniently referred to as DTA which is the terminology conventionally employed by those skilled in the art), for thermal mechanical analysis (dilatometer, penetrometer), for thermogravimetry and as calorimeters, to name only some of the most important apparatus of this group and their applications.
Hereinafter for the sake of simplicity reference will be conveniently only made to the case of DTA. It should be expressly understood, however, that all explanations and comments relating to the cooling system and its exchange action with the sample chamber temperature equally apply in principle with respect to the whole of the group of apparatus outline above.
Apparatus for DTA has been proposed for example in U.S. Pat. No. 3,456,490 for effecting DTA at low temperatures. It has been found, however, that when operating with such apparatus there are still some requirements which remain unfulfilled, for example as regards the control or regulation characteristic.
In the proposed apparatus of the prior art either the furnace heater of a heater for heating the cooling medium tank are switched-in in order to carry out a predetermined temperature program under the control of the temperature in the sample chamber. This arrangement allows for only a relatively coarse control or regulation with time-constants which are large (particularly when there are small differences between the reference or desired temperature and the actual temperature), that is to say, substantial delays occur when setting the desired temperature. The result of such delays, for example, is that alterations in the temperature gradient, which can influence the measurement result, can occur more easily in the sample chamber. Additionally, such delays limit the free choice of the program to be used as concerns sensitivity and speed, thereby restricting the capability of the apparatus.
A further difficulty concerns the supply of cooling medium or coolant. Previously proposed apparatus provide a respective cooling medium tank associated with each particular apparatus. This condition had to be fulfilled of necessity because of the operational link between the cooling medium heater and the temperature in the sample chamber. In many cases, however, it is desirable to render the apparatus independent of its own individual source of cooling medium. Thus, for example, it may be more economical for a plurality of apparatus to be connected to a common cooling medium tank, for example by way of a conduit network.